Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
943 PM CDT sun Mar 29 2015
Aviation/06z tafs/...as surface winds are becoming lighter this
evening...low level wind shear is possible due to a northwesterly 30-40 knots low level jet aloft. The
winds aloft will weaken sufficiently by 06z...the beginning of the
new taf period. Otherwise VFR conditions will prevail Monday into Monday
evening. A broken cloud deck of 7-9 kft is expected Monday afternoon into
the evening with small chances of very light rain...as low
Previous discussion... /issued 302 PM CDT sun Mar 29 2015/
Tonight...forecast confidence is medium.
A batch of rain showers is expected to shift east southeast through
the area late this afternoon. This second batch is being driven by a
secondary 500 mb vorticity maximum...sliding southeast through
Minnesota. The showers should exit the east by early this evening.
Cold front will move east through the area into early this
evening...shifting the gusty southwest winds to the west in its
wake. The pressure gradient is expected to slowly weaken
tonight...allowing the gusts to subside soon after midnight.
Any lingering low clouds into the early evening will gradually move
out of the area during the overnight hours. Lows tonight should drop
into the upper 20s to lower 30s...perhaps even colder if winds
weaken enough later tonight.
Monday...forecast confidence is medium.
Models are in decent agreement with high pressure ridge axis
shifting east into the region during the morning. GFS/European model (ecmwf) are
showing light quantitative precipitation forecast developing during the afternoon...as a warm front
develops just southwest of the area. The Canadian model is less
aggressive with the quantitative precipitation forecast...and the NAM is dry.
All models are showing a 500 mb vorticity maximum sliding southeast
into Wisconsin during the later portion of the day. There is some
focused warm air advection in the area...with some decent
frontogenesis response on the GFS. The NAM is much weaker. Area
forecast soundings are showing some saturation above 5000 feet above
ground level...dry below it.
Some uncertainty here...so will go with lower end probability of precipitation for light
rain Monday afternoon in the northern and central portions of the
area. Highs with the warm air advection should reach into the lower
to middle 50s.
Monday night and Tuesday...forecast confidence high.
A jet maximum over northern Minnesota moves through southern Wisconsin
Tuesday in the northwest flow...as a 250 mb upper ridge moves
into the Dakotas. The upper level divergence increases Monday
night and continues in the morning over the southeast on Tuesday.
850/700 mb warm air advection occurs Monday night before cooling
Tuesday at 850 mb...after the low/middle level trough moves off.
Weak 700 mb upward motion occurs early Monday evening before
increasing to moderate values mainly from north of Milwaukee and
across east central Wisconsin. 700 mb relative humidity is nearly saturated
Monday evening before strong drying from the west occurs late. 850
mb layers are dry until some moistening occurs from the north
Tuesday bringing a potential band of shallow stratocumulus.
However with mixing this may stay scattered.
The GFS is dry Monday evening but the European model (ecmwf) brings precipitation
to all but the far southwest areas...with the NAM mainly dry
except north toward Sheboygan. Given the surface and 850 mb
temperatures...it would be rain if it happens. Once the low exits
southern Wisconsin Monday night...weak high pressure will then
drift through the region Tuesday.
Tuesday night and Wednesday... forecast confidence high.
The upper ridge moves across Wisconsin Wednesday. 700 mb upward
motion starts Wednesday afternoon as the upper level divergence
increases over the north and west areas of the forecast area. The
higher 700 mb relative humidity stays just to the north and west through the
As the high recedes east Tuesday evening...moderate to strong
warm air advection occurs in the 925/850700 mb layers. The models
keep most of the showers off to the west and north through
Wednesday afternoon...except possibly the far northwest towards
and north of The Dells.
Wednesday night and Thursday... forecast confidence high.
A northern stream shortwave exits the northern plains Wednesday
evening...and moves across the Lake Superior area Thursday. A
southern stream shortwave digs across the western U.S. At the same
A mild south flow continues Wednesday evening until a cold front
moves east across southern Wisconsin late Wednesday night and
Thursday. The European model (ecmwf) is a little slower with the cold front and
precipitation...which will occur as rain.
Friday and Saturday... forecast confidence medium.
The models are more in line with the European model (ecmwf) trending toward the
GFS. As the northern stream shortwave lifts northeast into
Canada...the southern stream trough moves into and across the
Great Lakes. Both the GFS and European model (ecmwf) keep most of the precipitation
to the south and east. There will be a small chance of snow
showers with the main trough Saturday.
Sunday... forecast confidence medium.
A west/southwest middle and upper flow develops across the plains and
Great Lakes with a trough beginning to dig across the West Coast
of the U.S.
Both the GFS and European model (ecmwf) bring warm air advection Saturday night and
Sunday...with the European model (ecmwf) giving some light precipitation which
would likely be a mix. The GFS is dry as both models keep a
developing low near eastern Colorado.
A batch of light rain showers will move east southeast through the
area late this afternoon. May see MVFR visibilities with the
showers...with MVFR ceilings remaining. The showers should move east
of the area by early this evening.
Gusty south/southwest winds will veer west behind cold front by
early this evening. Gusts to 35 knots are possible at times before
the front moves through. West winds will gradually weaken later
tonight...as high pressure well to the south brings lighter winds.
MVFR ceilings will gradually move east of the area as well by later
West winds will become southwest later Monday afternoon. Warm front
trying to set up near the area should help bring some middle level
clouds...along with small chances for light rain. For now...will
leave mention out of tafs.
Gale Warning remains in effect until 7 PM this evening across the
nearshore waters of Lake Michigan. Area forecast soundings near
and over the lake showing gusts remaining up to 35 knots late this
afternoon...as tight pressure gradient remains over the region.
High waves of 5 to 7 feet are expected as well.
A Small Craft Advisory will be needed tonight...after the Gale
Warning expires...as the pressure gradient slowly weakens. Gusty
west winds to 30 knots will slowly weaken...with waves slowly
subsiding as well.
Lm...Small Craft Advisory until 4 am CDT Monday for lmz643>646.
tonight/Monday and aviation/marine...wood
Monday night through Sunday...hentz